Most clinical diagnostics and basic research studies aimed at understanding the causes underlying disease require isolation of specific biomolecules or cells from complex samples such as blood, saliva, and cell culture supernatant. Sometimes such bioparticles of interest are present in the samples in very small quantities. This is the case, for example, of antigen-specific T-cells, circulating tumor cells, and HIV viral particles, which can be used, for example, for monitoring immune responses, cancer, and AIDS progression respectively.
Fluidic (macroscopic) and microfluidic devices can be used for detecting, capturing, separating, and enriching particles of many types that are suspended or dispersed in a fluid. In some cases, microfluidic devices include obstacles coated with binding moieties that selectively bind to specific bioparticles that contact surfaces of the obstacle. In some situations, the obstacles are formed from solid materials such as silicon, polymers, and glass. Such materials possess attributes including geometrical definability (e.g., using photolithography), and compatibility with both gas and liquid-phase chemical functionalization processes. Geometrical definability, e.g., in microfluidic applications, allows control of the fluid dynamics inside the channels. Selective functionalization of the structural features allows isolation and manipulation of specific particles. In addition, some of the materials, such as polydimethylsiloxane (PDMS), exhibit optical transparency, which allows on-line visual monitoring of the tests and simplifies bio-assay readout designs.
However, in such prior devices, fluid-boundary interactions at the surface of obstacles in the fluid path can have detrimental effects on the desired functions of these devices.